Shell mold construction with chill plate having uniform roughness



July 7,' 1970 a. J. PIEARCEY 3,

SHELL MOLD CONSTRUCTION WITH CHILL PLATE HAVING UNIFORM ROUGHNESS FiledJuly 18, 1 968 2 Sheets-Sheet 1 By M B. J. PIEARCEY 3,519,@63 SHELL MOLDCONSTRUCTION WITH CHILL PLATE HAVING UNIFORM ROUGHNESS 2 Sheets-Sheet 2Filed July 18 F/G. Z

United States Patent SHELL MOLD CONSTRUCTION WITH CHILL PLATE HAVINGUNIFORM ROUGI-INESS Barry J. Piearcey, Galmpton, Brixham, Devon,England,

assignor to United Aircraft Corporation, East Hartford, Conn., acorporation of Delaware Continuation-impart of application Ser. No.472,611,

July 16, 1965. This application July 18, 1968, Ser.

Int. Cl. B22c 9/02; B22d 15/02 U.S. Cl. 164353 Claims ABSTRACT OF THEDISCLOSURE This invention relates to a chill plate for use in makingdirectionally solidified castings and castings in which the crystallinestructure is directionally oriented. The chill plate is used with atemperature-controlled shell mold which heats the casting material andestablishes a unidirectional temperature gradient between the materialand the chill plate. The surface of the chill plate in contact with thematerial is roughened to improve heat transfer to the plate and topromote directionally oriented crystalline growth or columnar graingrowth within the material.

This is a continuation-in-part of Piearcey Ser. No. 472,611, filed July16, 1965, now abandoned.

BACKGROUND OF THE INVENTION One feature of this invention is a chillplate construction that will facilitate the production of this type ofcasting. Another feature is a surface treatment of the chill plate toimprove the start and continued growth of the columnar grains.

The growth of the columnar grains is promoted by rapid heat removalthrough the chill plate and a feature of the invention is a roughenedchill plate surface thereby increasing the surface area of the plate incontact with the metal being cast. It has been found that thecrystalline growth with the desired orientation can be substantiallyimproved by more rapid heat dissipation into the chill plate.

Other features and advantages will be apparent from the specificationand claims, and from the accompanying drawings which illustrate anembodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view through amold embodying the invention.

FIG. 2 is an enlarged fragmentary vertical sectional view through achill plate having a smooth surface, and part of a casting thereon.

FIG. 3 is an enlarged view similar to FIG. 2 but in which the chillplate has a roughened surface.

FIG. 4 is an enlarged sectional view on a smaller scale of a portion ofthe surface of a modified form of chill plate.

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FIG. 5 is a plan view of a modified form of chill plate.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is for useprimarily in making directionally solidified castings as described inthe above-identified VerSnyder patent and in making single crystalcastings as described in the above-identified Piearcey application. Thepurpose of this invention is to facilitate the production of suchelements as turbine blades or vanes such that the orientation of thecrystallization will have a preferred relation to the longitudinal axisof the cast element or such that the grain boundaries also will have apreferred relation to this same axis.

Referring first to FIG. 1, the mold is shown as a shell mold 2positioned with the bottom opening 4 thereon resting on a chill plate 6.The shell mold may be arranged to produce a plurality of turbine bladesor vanes at one time and to this end incorporates a plurality ofvane-shaped'recesses 7 in parallel vertical arrangement. These recessescommunicate at the lower ends with growth area recesses 8 and at theirupper ends with top filling areas 10. These latter areas connect throughlateral passages 12 with the central pouring sprue 14 by which all therecesses 7 can be filled simultaneously.

The mold, when completed and ready to be used for casting structuralparts, is positioned within a ring or cylinder of heating elements 16 asdescribed in the copending application of Barrow and Sink, Ser. No.472,644, filed July 16, 1965, now Pat. No. 3,405,220 issued Oct. 8,1868, and having the same assignee as this application. These heatingelements provide for heating the mold to a temperature above the meltingtemperature of the alloy and are preferably arranged to be successivelyturned off during the casting process.

According to the present invention the chill plate 6 which has coolingmeans therein such as the cooling passages 17 has a roughened surface 18contacting with the mold and with the molten metal when it is pouredtherein. The roughness may be obtained by forming a plurality of grooves20 therein as in FIG. 4 or by knurling 22 as in FIG. 5 to provide asubstantially larger area of contact between the chill plate and themolten metal. The grooves 20 of FIG. 4 may be rectilinear groovesparallel to one another or may be annular or spiral grooves to producesubstantially the configuration shown. The most effective groove is thatmade with a threading tool producing a N.C. thread and the grooves arepreferably about one-sixteenth inch apart. The tool cut is deep enoughto leave lands or flats about .02 inch wide and the depth of the grooveis about .05 inch. Grooves spaced as closely as one-thirty-second of aninch with much narrower lands produces a finer grain structure and morewidely spaced grooves and thus wider lands produces a faster graingrowth. Thus the range of groove spacing may be as much as between onethirty-second and one eighth of an inch and the depth of the groove maygo from .03 to .10 inch, the depth being preferably about .05 inch. Thelands may vary from .01 to .045 inch in width and still be effective.

As above stated these grooves may be circular or rectilinear or they maybe comparable to a knurled surface with the grooves intersecting at anangle to one another varying from a 45 angle to a angle. The landsproduced by the intersecting grooves are preferably from .01 to .04 inchin width, the most effective being about .02 inch. As the chill plate isused repeatedly in producing cast articles, the grooves and lands mustretain their effectiveness over an extended use and for durability, whenthe sides of the grooves approach that of an N.C. thread the land widthof from .01 to .03 inch is most effective in repeated castingoperations.

The spacing, depth and shape, as above described, produces aneffectively greater contact surface than a flat plate to produce moreeffective heat transfer to the plate. With a depth of groove asdescribed, the mold contact with the chill plate requires no particularsealing arrangement since the immediate cooling of the molten metal asit contacts the chill plate effectively seals any of the small spacesthat might exist.

FIGS. 2 and 3 show graphically the improvement in cast structures withthe roughened chill plate. These views are about fifty times normalsize. In FIG. 2 it is apparent that the crystalline growth is randomrather than directional and no directional growth becomes establishedfor a substantial distance from the chill plate. However, with a chillplate as in FIG. 3, the directional crystalline growth begins at thepeak or top surfaces of the ridges in the chill plate and a directionalgrowth substantially at right angles to the plate is well establishedalmost immediately. The view of FIG. 3 was made after the grooved platehad been used for several castings and the lands had been eroded away tosome extent.

In addition to the directional growth being well established it has beenfound that the roughened chill plate surface improves materially theheat transfer from the melted alloy to the chill plate so thatsolidification occurs at a substantially faster rate than is the casewith a smooth plate. It has been found that the desirable properties inthe finished part are best obtained with rapid solidification and theroughened plate contributes to this effect.

It is well known that the rate of thermal conductivity is much less inthe well-known alloys used in high temperature environments such as gasturbine vanes and blades, than in other simpler metals that would beused in chill plates. The ability of the chill plate to remove heatfaster by its roughened surface helps to maintain a higher temperaturegradient in the article being cast and thus increases to an optimum theeffective rate of heat transfer lengthwise of the blade or vane andthence into the chill plate.

With the nickel or cobalt base superalloys which have beenunidirectionally solidified, it has been found that the l direction ofgrowth produces the crystalline orientation for optimum properties.During solidification the dendrite crystals grow fastest in the 00ldirection and under the temperature gradient resulting from a heatedmold and a chill plate this growth is substantially perpendicular to thechill plate surface. This temperature gradient is effectively measuredby the increase in surface area resulting from the grooves formed in thesurface. The roughness also serves to provide a more effectivemechanical joint so that casting and chill plate stay in better contactduring the solidification process.

The grooves increase the number of dendrites per unit area by a factorof more than two. This promotes the possibility of obtaining anorientation closer to 00l Further, as shown in FIG. 3, a greaterproportion of the dendrites are oriented substantially perpendicularlyto the 4 chill plate than where the surface of the chill plate issmooth.

When single crystal particles are cast, the first dendritic growthoccurring at the chill plate is directionally oriented in the samemanner as above described and the grooved chill plate is thus equallyeffective in establishing the properly oriented dendritic growth insingle crystal parts.

The grooved chill plate by measuring the rate of cooling has effectivelyreduced the size of the carbides in the alloy. These zone carbidesaffect the machinability of the alloy, particularly in electrochemicalmachining of the alloy and thus the parts produced by the use of theroughened chill plate has improved machinability substantially.

I claim:

1. In a mold construction for use in casting directionally solidifiedarticles, a temperature-controlled shell mold having a pouring spout, amold cavity open at the end opposite to the spout, and a chill plateclosing said open end, a portion of the plate thereby contactingdirectly with the material poured into the mold to form the article,said plate having a controlled substantially uniform roughness formingsubstantially fiat surface lands from .01 to .045 inch in width over theportion adapted to contact with the poured material to improve the startand continued growth of columnar grains within the material, said plateadapted to substantially retain said uniform roughness throughout thecasting operation.

2. A mold construction as in claim 1 in which the roughness is between.03 to .10 inch in depth.

3. A mold construction as in claim 1 in which the roughness is formed bysubstantially parallel uniform grooves having a depth of between .03 and.10 inch and spaced apart to form said lands.

4. A mold construction as in claim 1 in which the roughness is formed byintersecting grooves spaced apart to leave said lands.

5. A mold construction as in claim 4 in which the grooves are spacedabout one-sixteenth inch apart.

References Cited UNITED STATES PATENTS 1,727,565 9/1929 Schall 1643532,951,272 9/1960 Kiesler 164127 X 2,970,075 1/ 1961 Grenoble.

3,366,362 1/1968 Chandley et al. 164-60 X 3,248,764 5/1966 Chandley164-127 FOREIGN PATENTS 416,784 7/ 1925 Germany.

OTHER REFERENCES Transactions of the Metallurgical Society of AIME,volume 224, December 1962, pages 1271-1277.

ROBERT D. BALDWIN, Primary Examiner U.S. Cl. X.R. 164-361

